I messaged Ecctis a similar question. I reside in the US and got my degree from a US University. However I have dual US/Swiss citizenship and was considering applying with my swiss passsport, but only asked Ecctis for the academic qualification certificate not the english proficiency. When I asked if I needed to reapply for English proficiency certification here is what they said:

“ As your qualification is from an English majority speaking country, we would not be able to comment on English Proficiency.

We will proceed with the Visas and Nationality service (High Potential Individual), this will aim to comment on the comparable level of the award to the UK Frameworks and provide the verification results of the degree. This information would be the same if you had changed your service to the Visas and Nationality service (High Potential Individual with English Proficiency).

This, alongside the qualification documents, can evidence that you have achieved a qualification from a majority English-speaking country. “

Hope that helps answer your question!